My front wheel was not rotating freely so I figured I'd check the pistons out and give them a clean-up as I thought dirt or the seals were preventing them from retracting properly.
The calliper was very difficult to slide off and the pads were worn down but still had a little left.

I took the pads out and squeezed the brake lever to get the pistons to pop out.

I tried to get both of them to come out at the same time by using a brake pad to prevent one from coming all the way until the other popped out but alas, one came out completely while the other was sill in there. I read you need to get the two to come out at the same time.

Also got brake fluid everywhere as I am a complete novice and did not realise this would happen.

I read you could use compressed air to get them out so with the fluid now drained, I put the piston back in and tried to use a can of air on the bleeder valve. The tube from the can of air was not tight in the valve so this did nothing apart from probably getting some propellent liquid into the system. Don't know how bad this is....

I next tried to refill the brake system with brake fluid and try and pump the pistons out again.

I filled up the brake fluid reservoir put the cap back on and pumped the lever.
This had no effect so I opened up the bleeder valve and pumped the lever again until brake fluid started coming out.

I then closed the valve and pumped the lever again (over 300 times).

The pistons have not moved. Don't know what to try at this stage....

I'm thinking...maybe I should push the pistons back all the way in before trying to fill the system with brake fluid again and pumping them out with the lever?

Here's a pic what it looks like currently, any help would be appreciated:

No doubt there will be a someone here who can solve your dilemma with home workshop methods. ..

If I got to that stage though and wasn't sure if it was possible. .. personally I'd take the thing off the bike and down to the local brake mechanic, have him (or possibly her these days!) check/remove/replace the pistols and seals for a modest fee. .. you might be able to ask if you can watch/learn how its done to avoid catastrophy later times.

I'm not having a chip at you..  I know I cab fix some things and some I take to a shop!

Well theyre almost all the way out. just grab and pull em the rest of the way out. I dont think theres any reason that they both need to come out at the same time.

Clean stuff up and see what kind of shape the piston and bores are in.
Also drain all the old brake fluid.
If the pistons and bores look good order up some new seals and install in the caliper. Then grease the piston and push those back in (make sure the bleeder is open at this point.)
Install some new pads and bolt the caliper back on the bike.
Make sure to grease up the slider pins on the caliper so it slides back and fourth easily.

Then start filling. I suggest gravity bleeding at this time, let it sit till you some fluid comes out of bleeder. After that start bleeding it normal procedure, till you get all the air bubbles out and the lever has good feel.

Enjoy fresh brakes!

Thanks, some new pads, seals, fluid and a braided hose are on order. I plan to clean out the calliper and bores completely before installation. 

You say I should be able to just grab and pull them but with what would you suggest? a pliers wrapped in cloth perhaps? 
I was worried about damaging them to give them a good pull. I couldn't manage by hand. 

The pistons do look ok but I'm going to wait until I get them out completely before I make a decision about whether to replace them.

Also re: the grease...Is copper grease ok? That's what I have here.

I also bought an rubber valve for pumping up air beds. It attaches to a standard bike-pump. My  plan was to screw down the resevoir, and attach it onto the bleeder valve and try to pump the pistons out. Does that sound like it could work?

I'd think plyers with a rag should work. just make sure not to mar up the piston.

Fill the master with fluid, put a hose on the bleeder and run it back to the master reservoir. With both pistons in the caliper pump the brake lever until the hose on the bleeder has no more air in it.

Use the old brake pads as a spacer on the piston that would come out to limit its travel. If necessary to keep that piston in place add something between the brake pads.

You should be able to push out the stuck piston.

The bleeder needs to be the highest point for the air to bleed out.

regards
mech

Well Toner?

Did ya get those brakes up a running?... Or should I say Stopping.?

wasn't ever able to get the pistons out. Tried gripping them with a cloth an pliers but they weren't coming and I was scared of damaging them.

I bought an air bed nozzle and tried to attach it to the bleeder valve but it was too small and was made of hard plastic instead or rubber like I hoped. I bored it out with a drill but then it was too big.
I would like to try this method again with a different nozzle though. It sounds like it could be successful.

Before ordering anything again though, I just took it to a garage. He got them out but wouldn't tell me with what tools, just that he pulled them both at the same time.

Looks to me like the two toppest seals are completely disintegrated which was what was causing the problem.

I bought some brake cleaner and I'm going to give everything a clean.

Was wondering about this bit of rubber:



Any particular way to get it out and in again? I was going to just pinch the end and yank it through, maybe used a stick to push it back in again?

Any tips on cleaning too? I was going use a plastic spoon or similar to get the seal beds clean and just spray brake cleaning goo everywhere and let it set for a while and rub everything down.

Anything I should know?

I was wondering too about the sort of springy plate (not sure the name) the pistons come out over. Can this be removed?  Fair bit of grime under it I want to get at.
 

alright guys, seem to have hit an impasse here with my front brake. Here's what my current fix-up looks like: 



I got the pistons out, bought new ones with seals, gave everything a clean and inserted them, pushed them back into place, put on new pads, then attached the caliper to the fork, put on a new steel braided brake line and started the bleed process.

Couldn't get it going the old fashioned way so I bought a vacuum gun.
That sort of worked well enough but as the flask you see in that picture collecting the fluid has a tube going to the base of it, once the the fluid had covered the opening in that tube in the bottle, I was able to just open the bleeder valve and pump away as air would not be sucked back into the system.

I have pumped through about 8 brake cylinders of bubble-less fluid at this stage and am nearing the end of my bottle. The bleeder valve is currently closed.
There have been no visible bubbles in the tubes coming out of the bleeder valve when I pumped the brake lever yet the brake lever is not stiff. It is a little stiffer than when I started though.

What am I doing wrong? Am I missing something? If I continue to pump liquid out of the system with the lever, will it eventually become stiff?
I feel like I'm missing something or I did something wrong.

Really grateful for any help. Been weeks now without my bike after I've ordered part after part in the mail.

Is your brake cable adjusted properly? Is the cable streched? Did you ream the piston cylinders?

Is the what what?? 

Wow, what a nightmare this simple job has become.    I pop my pistons out of the calipers every time I replace brake pads, riding year around here in NE Ohio a hard crud builds up on the extended parts of the pistons that won't be removed by the outer wipers and will cause piston binding if not removed.  I pop the cylinders and clean them completely with SOS type pads or those green kitched pads.  I throw away those outer wipers some call seals because they won't remove anything but dust when pushing the pistons in.  They are not needed when pushing clean pistons in.

Fill as you go in brake work so I fill the caliper bores with fluid up to the seals and lube the pistons with brake fluid and push them in just past the inner seal. With both in place I hold the caliper upright, open the bleeder screw, push the pistons all the way in, and close the bleeder.  Then I put caliper back in place and it takes little bleeding to finish the job.

I don't normally remove the brake hose from the caliper when cleaning pistons and replacing pads.  If you have removed it and fluid has drained out of it while off then filling it with fluid will shorten the bleeding also.  Take the hose mid bracket loose and holding the end higher than the master cylinder with a thumb lightly over the end of the hose pump the fluid in until it comes thru without air.  Then put the full hose back on the caliper and very little bleeding should be needed to finish up with a hard lever.  Probably only a few strokes of the lever.   

Do it with the engine running, the vibes agitate the fluid and go some way in preventing air bubbles in the line from becoming lodged.

...and no, I didn't believe it either, until I actually tried it myself.

I'll post a proper update tomorrow guys but quick question:

When you read about putting a zip tie on the brake lever over night to leave it open and get air bubbles out that way, do you have to leave the cylinder top/cap off? 

Just want to let you all know what the problem was.

It was the bleeder screw. It needed replacement. I guess some of the threading was damaged.

I decided to go all out and buy a stahlbus Bleeder Valve
I bought mine from ebay uk but that is the US website. 

They are similar to a Speeder Bleeder^tm if you are familiar with them and take the place of your bleeder screw.
I think they are superior to speeder bleeders however as they have two nuts: 
One to tighten the device down into your caliper where it remains and second upper nut to open and close the valve.

When you want to flush brake fluid through the system (with a vacuum gun perhaps) , you turn the nut 1.5 times. 
When you just want to bleed the the brake system by pumping the brake, you turn the nut a half turn. 
You might be tempted to turn it more as you don't initially see brake fluid coming out but don't. Keep pumping your brake and the fluid will emerge.
They contain a one-way valve so you don't have to open and close it constantly like with a standard bleeder screw.

Very easy to use and I was able to get my brake system working successfully  .

The size Stahlbus bleeder valve the Suzuki GS500 takes is M7x1.0x16mm if anyone is thinking of getting one.
(Took me a while to figure that out)



Thank-you for all your help!

Good info!